Process for producing polyamine boranes

ABSTRACT

This invention relates to a process for producing tertiarydiamine-boranes by reacting a tertiary diamine with a borohydride in the presence of a carboxylic or mineral acid source. Water is included in the reaction medium in a catalytic amount but insufficient for forming two phases. Excellent selectivity to tertiary diamine-boranes is achieved.

TECHNICAL FIELD

This invention relates to a process for producing tertiary polyamineboranes by the reaction of a borohydride with a tertiary polyamine.

BACKGROUND OF THE INVENTION

Tertiary amine boranes are utilized in many fields, which include thepreparation of epoxy resins by acting as a curing agent or accelerators;in organic synthesis as reducing agent; as a reagent for thehydroboration of alkenes and in electroless plating applications.Essentially five methods have been developed for the synthesis oftertiary amine-boranes and these methods are described as follows:

1. The direct reaction of an amine and diborane;

2. Reacting tetrahydroborates with ammonium salts;

3. Transamination of aminoboranes;

4. The reaction of a metal tetrahydroborate with iodine in the presenceof an amine; and

5. The reaction of a metal tetrahydroborate with carbon dioxide orcarboxylic or mineral acid in the presence of an amine and organicsolvent.

Many of the above methods were difficult to practice in the productionof tertiary amine-boranes because of the required synthesis of variousreactive materials, the handling of expensive or difficult to handlereagents and difficulty in product recovery.

Of the above synthesis techniques, the one which appears to be mostwidely utilized is synthesis route 5 which involves the reaction of ametal borohydride with a tertiary amine. The following patents arerepresentative:

U.S. Pat. No. 3,013,016 discloses a process embraced within synthesisroute 5 for producing trialkylamine boranes. A trialkylamine, e.g.trimethylamine or triethylamine, is contacted with potassium borohydridein the presence of an aqueous phase containing an inert organic solventwhich is immiscible or only partially miscible with water. Carbondioxide, or an acid source such as a carboxylic acid or mineral acid isadded to the reaction medium. Reaction occurs at about 20°-40° C. andatmospheric pressure. The product is recovered by separating the organicsolution containing the trialkylamine borane for the aqueous phase andthen separating the organic solvent from the trialkylamine borane bydistillation.

Czechoslovakian patent 242,064 discloses a process for producingtertiary amine-boranes via synthesis route 5 wherein an anhydroussuspension of a metal tetrahydroborate and tertiary amine in an organicsolvent is contacted with carbon dioxide gas at temperatures rangingfrom about 0° to 50° C. for a period of 1-5 hours. The reaction productis washed with water, dried and the solvent evaporated.

British patent 909,390 discloses a process for producing amine boranesby reacting an amine salt with aqueous metal borohydride in organicsolvent at room temperature under neutral or alkaline conditions.Product recovery is accomplished by separating the amine borane as it isformed by separating organic solvent containing the amine borane fromthe aqueous layer and then distilling the solvent from the amine borane.

Taylor, et al. in J. Am. Chem. Soc., vol. 77, 1955, pp. 1506-7 disclosethe production of pyridine-borane complexes by reacting pyridinehydrochloride with sodium borohydride in the presence of pyridinesolvent. Byproduct sodium chloride precipitates and unreacted pyridinehydrochloride is precipitated by the addition of ether. Unreactedpyridine is separated from the pyridine-borane reaction product bydistillation.

SUMMARY OF THE INVENTION

This invention relates to an improved process for preparing amineboranes by the reaction of a metal borohydride with a tertiary amine inthe presence of an inert, water immiscible organic solvent and a proticacid source. The improvement for enhancing yields in the production ofthe amine borane complexes having a water solubility greater than about2 grams per 100 cc's at 25° C. and where the amine is a polyaminecontaining at least one tertiary nitrogen atom comprises effecting thereaction of the borohydride with the complex in the presence of water,wherein the water is present in a small but catalytically effectiveamount but insufficient for forming two phases. There are severaladvantages associated with the process of this invention. Theseadvantages include:

an ability to produce tertiary amine-borane in high yield;

an ability to produce a commercially desirable white solid as product;

an ability to produce tertiary amine-boranes in a one-pot synthesisapproach, and

an ability to separate the product from the reaction mixture withrelative ease.

DETAILED DESCRIPTION OF THE INVENTION

In the conventional preparation of tertiary amine boranes, a tertiaryamine or salt is reacted with a borohydride under modest reactionconditions. In this case the tertiary amines are polyamines containing atertiary nitrogen atom, e.g., diamines having from about 2-10 carbonatoms, which may be aliphatic or cyclic. Examples of tertiary aminesinclude N-alkylated polyamines, e.g. methylated and ethylatedderivatives of polyamines such as, ethylenediamine, propylenediamine,diethylenetriamine and triethylenetetraamine, e.g., methylatedethylenediamine or methylated propanediamine and methylatedtriethylenetetramine; cyclic amines, e.g. dimethylpiperazine,diethylpiperazine, triethylenediamine and methyltriethylenediamine; andether amines, e.g., dimethylaminoethyl ether and bis morpholinoethylether. Of these polyamines, triethylenediamine andmethyl-triethylenediamine are well suited for forming borane complexes.

The borohydrides which are reacted with the tertiary amine includealkali metal borohydrides such as sodium borohydride and potassiumborohydride and lithium borohydride. Borane may also be used.

To facilitate reaction between the tertiary amine and borohydride, thereactants are dissolved in an organic solvent which is inert to thereaction medium. Conventional organic solvents, which are suited forproducing tertiary amine boranes include hydrocarbons such as benzene,toluene, xylene; ethers such as diethylether, methodyethylether,dimethoxyethane, methyltert-butylether, dioxane, tetrahydrofuran andisopropyl ether; aliphatic hydrocarbons, i.e., those having from about 6to 20 carbon atoms, e.g., hexane, pentane, dodecane, and the like. Inaddition various carboxylic esters such as ethylacetate, propylacetateand the like and nitriles such as acetonitrile can be used. The organicsolvents used in the synthesis are well known and most will work so longas the reactant amine and product borane complex are soluble in thesolvent and sufficiently volatile such that they can be distilled awayfrom the reaction product.

The reaction of the tertiary amine with the alkali metal borohydride iscarried out in the presence of a protic acid source, e.g. a C₂₋₁₀,preferably a C₂ -C₄ carboxylic acid, or an anhydrous mineral acid.Examples of C₂₋₁₀ carboyxlic acid sources include, acetic acid,propionic acid, butyric acid and examples of mineral acids includehydrochloric, phosphoric and sulfuric acids. When using a mineral acidit may be necessary to dilute such acids in an organic solvent as theanhydrous, concentrated mineral acids may be too strong and causeproduct decomposition.

In contrast to previous processes, the reaction is carried out in thepresence of only a trace amount of water, i.e., sufficient water tocatalytically enhance the production of the tertiary amine boranecomplex but insufficient for forming two phases, e.g. the saturationlevel. Typically, the level of water will range from at least about 0.5%based on the weight of the solvent to the saturation point of water inthe solvent. This may be from 1.2% for ethyl ether to 0.6% for isopropylether to 1.5% for tert-butyl ether to 3.3% for ethyl acetate. Incontrast to the prior art processes water is to be avoided in thereaction and in product recovery in order to maximize the yield oftertiary amine boranes produced and to facilitate the recovery of thetertiary amine borane from the reaction medium. When excess water ispresent in the reaction medium, as evidenced by two phases with thewater immiscible organic solvent, yields typically drop because ofmovement of the tertiary amine borane from the organic solvent to theaqueous phase thus resulting in product loss. Although not intending tobe bound by theory it is believed that the tertiary polyamine or diamineresults in a more water soluble product than does the monoamine boraneand when present in a carboxylic acid containing aqueous medium thetertiaryamine borane is destroyed.

Temperatures required for reaction of the tertiary amine with the alkalimetal borohydride are conventional and typically range from about -25°to 30° C., preferably -15° to 15° C., with pressures ranging fromatmospheric to 50 psig.

The following examples are provided to illustrate embodiments of theinvention and are not an attempted to restrict the scope thereof.

EXAMPLE 1

Methyl-triethylenediamine (MTEDA) Borane In Presence of Water and anacetic acid suspension of 20 g NaBH₄ in 375 mL anhydrous diethyl ether(specified as containing <0.01% water) was cooled to 2° C. in a coolingbath. To this was added 61.5 g of freshly distilledmethyl-triethylenediamine (MTEDA, water content 600 ppm) and 1.5 mL H₂O. A solution of 30 g glacial acetic acid (99.7) in 30 mL anhydrousdiethyl ether was added to the stirred suspension at such a rate thatthe addition was complete in 70 minutes and the reaction temperature didnot exceed 5° C. The mixture was stirred an additional 40 min. at <5° C.and the cooling bath was then removed. Stirring was continued anadditional 45 min. as the temperature rose to 18° C. The reactionmixture was then allowed to stand overnight. At this time, the mixturewas filtered and the ether solution was removed to give 24.4 g ofMTEDA/BH₃ which was obtained as a white solid. The remaining solid fromthe filtration was washed thoroughly with toluene and the wash solutionwas taken to dryness to yield an additional 37 g of product. A productyield of about 87% was obtained.

EXAMPLE 2 Preparation of Methyl-triethylenediamine Borane in Presence ofAcetic Acid and water containing methyl-triethylenediamine

Approximately 200 mL anhydrous Et₂ O was placed in a flask and the flaskwas purged with N₂ for ˜15 minutes. To this was added 19 g NaBH₄. Themixture was cooled to 0° C. with an ice bath and 63 g of crude MTEDA(˜2.5% H₂ O content) was carefully added while observing thetemperature. A solution of 30 g of glacial acetic acid in 30 mLanhydrous ethyl ether was prepared and placed in an addition funnel thatwas then placed on the flask. The amount of ether in the reaction flaskwas then adjusted so that it was approximately 250 mL. The acetic acidsolution was slowly added, while stirring vigorously, over a period of75 minutes at such a rate so as to maintain the reaction temperature at3°-7° C. Vigorous gas evolution was noted. After the addition wascomplete, the temperature fell and the gas evolution slowed. Stirringwas continued for 30 minutes and the temperature was slowly raised toroom temperature. The flask was kept under a slow N₂ purge overnight.The next day, the solid residue was extracted with a total of 800 mLether and 600 mL toluene. The extracts were dried to give a total of62.5 g of waxy yellow solid (89% yield). This procedure gave yields of69-92% (five runs) on this scale and 79-88% (four runs) when run attwice the scale. Yields were excellent.

This example shows that trace amounts of water can be added to thereaction medium by addition with the methyl-triethylenediamine feed incontrast to being added as a separate component as illustrated inExample 1.

EXAMPLE 3 Preparation of Methyl-triethylenediamine in Presence of AceticAcid in Anhydrous Medium

The procedure of Example 1 was repeated except that the 1.5 ml H₂ Owater addition was omitted. Glacial acetic acid was used as the proticacid source. A clear, colorless, liquid, as opposed to the white solidobtained in Example 1 was obtained. The liquid product was analyzed by¹³ C NMR and analysis showed the liquid consisted of a 1:1 mixture of amethyl-triethylenediamine/BH₃ complex and an acetyl containing impurity.

EXAMPLE 4 Preparation of Methyl-triethylenediamine Borane in Presence ofCO₂ in Anhydrous Medium

Methyl-triethylenediamine (63 grams) was charged to a vessel along witha suspension of 19.5 grams sodium borohydride in 300 mL's anhydrousacetonitrile. Carbon dioxide was bubbled through the suspension, whilestirring, for about 90 minutes. The temperature was maintained at20°-25° C. during the reaction period. A white product was obtained inabout 87% yield.

This example, in contrast to Example 3, showed that CO₂ was effectivefor effecting the reaction between methyl-triethylenediaine and sodiumborohydride in an anhydrous medium while the protic acid, glacial aceticacid, was ineffective. The by-product acetyl containing impurity was notpresent when CO₂ was used as the reactant and it was concluded thereaction was by a different mechanism than that when protic acid wasused.

EXAMPLE 5 Preparation of Methyl-Triethylenediamine Borane in Aqueous TwoPhase in Presence of CO₂ (Comparative Method of Haberland and Stroh,U.S. Pat. No. 3,013,016)

A mixture of 20 mL H₂ O and 500 mL hexane was placed in a flask andpurged with a flow of N₂. The flask was placed in an ice-bath and asolution of 40 g of NaBH₄ in 200 mL of H₂ O was added. Purging wascontinued and 127 g of MTEDA was added. Two phases were present. Carbondioxide was bubbled through the mixture for ˜6 hours with vigorousstirring. At the end of this time, the mixture was allowed to settle forca. 1 hour. Extraction of the aqueous slurry with 2×100 mL ethyl ethergave a yellow hexane/Et₂ O solution which was evaporated to dryness togive about 5 g of a sticky yellow solid (ca. 5% yield).

This Example shows that reduced yields were obtained at the higher waterlevel (compare Example 2). Apparently, the water interfered with theisolation.

In the conventional process of U.S. Pat. No. 3,013,016 conversion oftrimethyl and triethylamine to a borane complex could be effected usingCO₂ in a two phase process. In contrast, the amine borane yield wasquite low when a polyamine containing a tertiary nitrogen atom, i.e.,methyl-triethylenediamine was used. Lower product yields are believed tobe caused in part by inseparability of the product due to solubility ofthe product in the reaction mixture.

What is claimed is:
 1. In a process for producing amine boranes by thereaction of a metal borohydride with a tertiary amine in the presence ofan inert organic solvent and a protic acid source, the improvement forenhancing formation of a borane complex of a polyamine containing atertiary nitrogen atom as the tertiary amine which comprises:effectingthe reaction in the presence of water wherein the water is present in acatalytically effective amount but insufficient for forming two phases.2. The process of claim 1 wherein the water is present in an amount offrom 0.5% based upon the weight of the solvent to the saturation level.3. The process of claim 2 wherein the acid source is a carboxylic acidwherein the carboxylic acid has from 2-10 carbon atoms.
 4. The processof claim 3 wherein said polyamine containing a tertiary nitrogen atom isa cyclized diamine.
 5. The process of claim 4 wherein said cyclizeddiamine is triethylenediamine or an alkyl derivative thereof.
 6. Theprocess of claim 5 wherein said cyclized diamine ismethyltriethylenediamine.
 7. The process of claim 3 wherein saidpolyamine is a methylated or ethylated derivative of diethylenetriamineor triethylenetetramine.
 8. The process of claim 3 wherein saidpolyamine is methylated ethylenediamine or methylated propanediamine. 9.The process of claim 2 wherein said acid source is a mineral acidcarried in an organic medium and said amine is triethylenediamine ormethyltriethylenediamine.
 10. A process for forming borane complex oftriethylenediamine and methyl-triethylenediamine which comprisesreacting methyl-triethyleneamine or triethylenediamine with sodiumborohydride in the presence of C₂₋₄ carboxylic acid and water whereinthe water is provided at a level of from 0.5% by weight of the amine tothe saturation level, the reaction being carried out at a temperaturefrom about -25° to 30° C. and a pressure ranging from atmospheric to 50psig.
 11. The process of claim 10 wherein said carboxylic acid is aceticacid.